Chromate Reduction by Chromium‐Resistant Bacteria Isolated from Soils Contaminated with Dichromate

Abstract

Extensive use of hexavalent chromium [Cr(VI)] in various industrial applications has caused substantial environmental contamination. Chromium-resistant bacteria isolated from soils can be used to remove toxic Cr(VI) from contaminated environments. This study was conducted to isolate chromium-resistant bacteria from soils contaminated with dichromate and describes the effects of some environmental factors such as pH, temperature, and time on Cr(VI) reduction and resistance. We found that chromium-resistant bacteria can tolerate 2500 mg L(-1) Cr(VI), but most of the isolates tolerated and reduced Cr(VI) at concentrations lower than 1500 mg L(-1). Chromate reduction activity of whole cells was detected in five isolates. Most of these isolates belong to the genus Bacillus as identified by the 16S rRNA gene sequencing. Maximal Cr(VI) reduction was observed at the optimum pH (7.0-9.0) and temperature (30 degrees C) of growth. One bacterial isolate (Bacillus sp. ES 29) was able to aerobically reduce 90% of Cr(VI) in six hours. The Cr(VI) reduction activity of the whole cells of five isolates had a K(M) of 0.271 (2.61 mM) to 1.51 mg L(-1) (14.50 mM) and a V(max) of 88.4 (14.17 nmol min(-1)) to 489 mg L9-1) h(-1) (78.36 nmol min(-1)). Our consortia and monocultures of these isolates can be useful for Cr(VI) detoxification at low and high concentrations in Cr(VI)-contaminated environments and under a wide range of environmental conditions.

Isolation and Characterization of Chromium(VI)-Reducing Bacteria from Tannery Effluents

“…Q5-1, Bacillus sp. ES29, Escherichia coli, Enterobacter cloacae, Pseudomonas fluorescens LB300 [3][4][5][6][7]. Application of Cr-resistant bacteria for detoxification of Cr(VI) has been considered as an economical, effective and safe procedure over conventional physical and chemical methods [8].…”

Redução de cromo hexavalente por bactérias isoladas de solos contaminados com cromo

“…A presença de sulfato de cobre estimulou a atividade de redução da maioria dos isolados, sendo esta 60% maior que o controle para o isolado 20. Este estímulo foi observado com adição de cloreto de cobre por CAMARGO et al (2003) e KEYHAN et al (2003), segundo os quais a atividade de redução do Cr(VI) pelo microrganismo avaliado foi estimulada pela adição de sulfato e cloreto de cobre. A atividade de redução do Cr(VI) pelos isolados 6 e 12 praticamente não foi estimulada pela presença de íons cobre.…”

“…Neste teste, os isolados foram comparados com o Bacillus sp. ES29, uma bactéria comprovadamente redutora de Cr(VI), isolada por CAMARGO et al (2003). Como inibidores, foram testados íons, adicionados à mistura de reação na forma de sulfato de cobre, cloreto de magnésio, cloreto de mercúrio, cloreto de manganês e sulfato de sódio, todos na concentração de 1mM.…”

Evaluation of Cr (VI) remediation potential of <i>Eichornia</i> sp in conjunction with chromium-resistant bacterial strains

“…Camargo et al stated that Pseudomomas flouresence along with Eihchornia sp. caused decrease in chromium content of effluent, whereas high quantity of chlorophyll was seen with increase in biomass of Eichornia within 20 days of incubation [21].…”